A seat belt system for an occupant of a motor vehicle normally comprises a belt, a retractor for winding up the belt, and means for locking the belt in a position wrapped around the seated occupant. In a seat belt system having a shoulder belt and a lap belt, the belt normally extends upwardly from the retractor to a D-ring adjacent to the occupant's shoulder, through the D-ring, and downwardly from the D-ring to an anchoring point at the outboard side of the seat. A buckle is connected to an anchoring point at the inboard side of the seat. A cinch tongue is carried on the belt between the D-ring and the outboard anchoring point, and includes a latch plate which is insertable for locking in the buckle. The retractor permits the belt to unwind as the occupant moves the cinch tongue across to the inboard side of the seat for locking in the buckle. A shoulder belt is thereby defined between the D-ring and the locked cinch tongue, and a lap belt is defined between the locked cinch tongue and the inboard anchoring point. The retractor winds up slack in the belt to draw the shoulder and lap belts firmly against the occupant. When the cinch tongue is unlocked from the buckle, the retractor winds up the belt to carry the belt and the cinch tongue back across the occupant toward the outboard side of the seat.
The cinch tongue should slide along the belt when the occupant moves the cinch tongue in the inboard direction toward the buckle. The cinch tongue should also slide along the belt after the occupant unlocks the cinch tongue from the buckle so that the retractor can fully wind up the belt. The retractor would otherwise carry the cinch tongue upwardly to the D-ring, whereupon further movement of the belt would be prevented as the D-ring blocked further movement of the cinch tongue. Conversely, when the cinch tongue is locked in the buckle, it should clamp the belt against movement when the vehicle experiences a crash. Cinch tongues for vehicle occupant seat belt systems therefore include means for selectively clamping and releasing a seat belt.
U.S. Pat. No. 4,551,889 shows a cinch tongue having a latch portion for locking in a buckle and a lock bar for clamping a seat belt against movement through the cinch tongue. The cinch tongue comprises an elongated plate. The plate includes the latch portion at one end of the plate, and an opening for a seat belt at the other end of the plate. A pair of spaced apart flanges extending from the upper side of the plate include surfaces which define a pair of opposed angular slots. An elongated lock bar extends across the cinch tongue between the flanges, with each opposite end of the lock bar received in a slot
A seat belt in an unclamped condition extends up through the opening in the plate, over the lock bar in a forward direction, and back down through the opening in the plate to continue in a forward direction past the latch portion of the plate. When the seat belt and the cinch tongue are moved into a position wrapped around a seated occupant, the forward portion of the seat belt is folded back toward the rear of the cinch tongue to wrap the seat belt around the lock bar. The lock bar is slidable in the slots so that tension in the folded-back portion of the seat belt pulls the lock bar to slide rearwardly in the slots and to pivot through the angular turns in the slots. Rearward movement of the lock bar in the slots causes the rear edge of the lock bar to draw the seat belt tightly against the rear edge of the opening in the plate. The seat belt is thereby releasably held against movement through the cinch tongue.
Another cinch tongue is shown in U.S. Pat. No. 4,291,918. The '918 patent shows a cinch tongue comprising a frame which has a locking tongue portion for insertion in a buckle, and a cinching member which engages a seat belt. The frame includes a pair of spaced apart flanges having opposed triangular apertures. The cinching member has end tabs received in the apertures for limited pivotal movement of the cinching member relative to the frame. A buckle for locking the cinch tongue in place includes a projection having a surface which is located opposite the cinching member when the cinch tongue is locked into the buckle. A leaf spring in the cinch tongue biases the cinching member to clamp a seat belt against the opposed buckle surface.